Correction to This Article
The A-section article about the melting of the polar ice caps misspelled the name of Ted Scambos?, a researcher at the National Snow and Ice Data Center at the University of Colorado at Boulder.

At the Poles, Melting Occurring at Alarming Rate

For scientists, global warming is a disaster movie, its opening scenes set at the poles of Earth. The epic already has started. And it's not fiction.

The scenes are playing, at the start, in slow motion: The relentless grip of the Arctic Ocean that defied man for centuries is melting away. The sea ice reaches only half as far as it did 50 years ago. In the summer of 2006, it shrank to a record low; this summer the ice pulled back even more, by an area nearly the size of Alaska. Where explorer Robert Peary just 102 years ago saw "a great white disk stretching away apparently infinitely" from Ellesmere Island, there is often nothing now but open water. Glaciers race into the sea from the island of Greenland, beginning an inevitable rise in the oceans.

Animals are on the move. Polar bears, kings of the Arctic, now search for ice on which to hunt and bear young. Seals, walrus and fish adapted to the cold are retreating north. New species -- salmon, crabs, even crows -- are coming from the south. The Inuit, who have lived on the frozen land for millennia, are seeing their houses sink into once-frozen mud, and their hunting trails on the ice are pocked with sinkholes.

"It affects everyone," said Carin Ashjian, a Woods Hole Oceanographic Institute scientist who spent early September with native Inupiats in Barrow, the northernmost town of Alaska. "The only ice I saw this year was in my cup at the cafeteria."

At the South Pole, ancient ice shelves have abruptly crumbled. The air over the western Antarctic peninsula has warmed by nearly 6 degrees since 1950. The sea there is heating as well, further melting edges of the ice cap. Green grass and beech trees are taking root on the ice fringes.

Antarctica's signature Adelie penguins are moving inland, seeking the cold of their ancestors, replaced by chinstrap and Gentoo penguins, which prefer open water. Krill, the massive smorgasbord for a food chain reaching to the whales, are disappearing from traditional spawning grounds.

"We've seen quite big changes in the living environment," John King, a lead researcher for the British Antarctic Survey, said from Cambridge, England.

The scenario is not new. What is most alarming to the scientists is the speed at which it is unfolding. A decade ago, melting at the poles was predicted to play out over 100 years. Instead, it is happening on a scale scientists describe as overnight.

When the Larsen B, an Antarctic ice shelf the size of Rhode Island, collapsed in 2002, "it was a big glaring clue that something not natural was happening," said Hugh Ducklow, director of ecosystems for MBL Laboratories in Woods Hole, Mass. "The geological evidence suggested that was stable for at least 10,000 years, back to the last ice age. And it literally disintegrated in three weeks."

The scientists say the coming scenes in the movie, as described by the historic melding of research assembled by the Intergovernmental Panel on Climate Change, will be even more disturbing: